Hi, 

 I given my full code below:

public with sharing class Facebook {

public string accessToken { get; set; }
public string clientID = '213658272132885';

public string clientSecret = 'efe8672baab3a0ef1c7025def208042f';
public string code { get; set; }
public string status { get; set; }
public string authuri;

public string statusupdate { get; set; }
public string facebookUname { get; set; }
public string facebookId { get; set; }
public string facebookEmail { get; set; }
public string facebookBio { get; set; }
public list<Facebook__c> fb{get;set;}

public Facebook()
{

}


public PageReference connect()
{
PageReference p = null;

if (ApexPages.currentPage().getUrl() == '/apex/FBPage' ){
String rediruri = 'https://'+ApexPages.currentPage().getHeaders().get('Host')+'/apex/FBPage';
System.debug('host:'+rediruri);

authuri = 'https://graph.facebook.com/oauth/authorize?client_id='+
clientID+'&redirect_uri='+rediruri;
System.debug('URL IS in1at - :'+authuri);
p = new PageReference(authuri);
}

else if(ApexPages.currentPage().getParameters().containsKey('code')) //second req
{
System.debug('URI: '+ApexPages.currentPage().getUrl());

String CodeForFB = ApexPages.currentPage().getParameters().get('code');
System.Debug(' Code ------------ >2 '+CodeForFB);


String rediruri1 = 'https://'+ApexPages.currentPage().getHeaders().get('Host')+'/apex/FBPage';

authuri = 'https://graph.facebook.com/oauth/access_token?client_id='+
clientID+'&redirect_uri='+rediruri1+'&client_secret='+clientSecret+'&code='+CodeForFB+'&scope=read_stream,status_update,manage_pages,user_status,user_notes,publish_actions,offline_access,user_photos';
System.debug('URL IS:'+authuri);

doFinalHttpRequest(authuri);
}
return p;
}
private void doFinalHttpRequest(String uri)
{
Http h = new Http();

HttpRequest req = new HttpRequest();
req.setEndpoint(uri);
req.setMethod('GET');

HttpResponse res = h.send(req);


String resp = res.getBody();
System.debug('FINAL RESP IS:'+resp);
//token string in format of access_token=XXXXX&expires - we want the first value
String accesstoken = '';
if(resp.indexOf('&') > -1){
accesstoken = resp.substring(13, resp.indexOf('&'));
}
else {
accesstoken = resp.substring(13,resp.length());
}

System.debug('Access token:'+accesstoken);
accessToken = accesstoken;

System.Debug(' Access Token -----> '+accessToken);

UserDetail(accesstoken);
}
public void UserDetail(String Url){
Http h = new Http();

HttpRequest req = new HttpRequest();
req.setEndpoint('https://graph.facebook.com/me?access_token='+Url);
req.setMethod('GET');

HttpResponse res = h.send(req);

System.Debug(' Display Detail s---- > '+res.getBody());
String resBody = res.getBody();

String strSpan = 'name":"';
String TempString = resBody.substring(resBody.indexOf(strSpan));
system.Debug(' TempString '+TempString);

facebookUname = TempString.substring(strSpan.length(), TempString.indexOf('",'));
system.Debug(' facebookUname '+facebookUname);

String StrId = 'id":"';
String TempId = resBody.substring(resBody.indexOf(StrId));
facebookId = TempId.substring(StrId.length(), TempId.indexOf('",'));
system.Debug(' facebookId '+facebookId);

fb = new List<Facebook__c>();
fb = [select name,Access_Token__c,FacebookID__c from Facebook__c where name=:Userinfo.getUserId()];
system.debug('fb---'+fb);
if(fb.size()>0){
fb[0].Access_Token__c=Url;
update fb[0];
}
else{
Facebook__c fbn = new Facebook__c();
fbn.Name = Userinfo.getUserId();
fbn.Access_Token__c=Url;
fbn.FacebookID__c=facebookId;
insert fbn;
}
}

public void updatepost(){
string fid;
string token;
Map<String, Facebook__c> map_accesstoken = new Map<String, Facebook__c>();
map_accesstoken = Facebook__c.getAll();

if( map_accesstoken.containsKey( Userinfo.getUserId() )){
Facebook__c fb = map_accesstoken.get( Userinfo.getUserId());
if(fb.FacebookID__c!=null){
fid=fb.FacebookID__c;
token=fb.Access_Token__c;
}
}


Http h = new Http();

HttpRequest req = new HttpRequest();
req.setEndpoint('https://graph.facebook.com/'+fid+'/feed');
req.setHeader('access_token',token);
req.setBody('message='+statusupdate);
req.setMethod('POST');
HttpResponse res = h.send(req);

System.Debug(' resdata--- > '+res.getBody());
}
}

ERROR:

{"error":{"message":"(#200) This API call requires a valid app_id.","type":"OAuthException","code":200}}

In page one Textarea field is there to give any message and "submit" button is there to display that message in facebook userwall.

Thanks

Ranjith