LookupRows.amp

<script runat="server" language="javascript">
    Platform.Load("core", "1");
    try {
        var CheckDE = DataExtension.Init("DE_Name_TO_Check");
        var CheckDEStatus = CheckDE.Rows.Lookup(["FieldName"], [Value]);
</script>

    %%[SET @DEExists = "true"]%%

<script runat="server" language="javascript">
Platform.Load("core", "1");
    }
    catch (e) {
</script>

    %%[SET @DEExists = "false"]%%

<script runat="server" language="javascript">
Platform.Load("core", "1");
    }
</script>

This is to confirm if DE Exists: %%=v(@DEExists)=%%

%%[
if @DEExists == true then 
   var @rows
   set @rows = LookupRows('DE Name', 'Field', 'Value')
endif
]%%